The anterior cruciate ligament (ACL) is frequently injured in contact sports and other activities. Such injuries cause instability in the knee to an extent that ACL reconstruction may be required. Medical procedures have developed over the years to enable in ACL reconstruction, the substitution of a ligament or graft and attaching both ends thereof to the distal femur or proximal tibia to facilitate regrowth and permanent attachment. One method for increasing the strength of the graft attachment comprises wedging an interference screw between a graft bone block and an interior wall of a bore (osseous tunnel) formed through the bone mass. Tension forces applied to the graft after it has been attached to the femur and tibia are considerable and it is essential that the interference screw so utilized in the medical procedure have sufficient strength to resist the tendencies for the replacement ligament (graft) to pull out of the osseous tunnels formed in the bone mass.
Applicants have noted that the tendency for interference screws to pull out of the osseous tunnels when considerable forces are applied to the substitute ligament are caused in part by either weak bone structure or flexure of the thread design utilized on the interference screws. Thus, a need remains for a high strength interference screw for use in surgical procedures, such as ACL reconstruction.
Accordingly, it is an object of this invention to provide an orthopedic interference screw for compression anchoring a bone graft in an osseous tunnel formed in a bone mass.
It is a further object of the invention to provide an orthopedic interference screw for use in ACL reconstruction.
It is a further object of the invention to provide an orthopedic interference screw, as aforesaid, which is made of a biocompatible material and having a root with front and back ends and further including an outer surface with a uniform taper at a root taper angle to a longitudinal axis of the screw and the formation of a screw thread over substantially all of the root, the screw thread including crests with a uniform surface area along the length thereof and uniformly spirally expanding from the outer surface of the root over at least the front end of the screw so that an aggregate of the crests form at least at the aforesaid front end of the screw a crest taper angle greater than the root taper angle.
It is a further object of the invention to provide an orthopedic interference screw, as aforesaid, wherein the root has front and back ends and further includes an outer surface with a uniform taper at a root taper angle to a longitudinal axis of the screw between the front and back ends, wherein a screw thread is formed over substantially all of the root, the screw thread including crests with a uniform surface area along a length thereof and uniformly spirally expanding from the outer surface of the root from the front end to the back end so that an aggregate of the crests form a crest taper angle greater than the root taper angle, and wherein the screw thread includes a buttress construction on only one side of the screw thread capable of reinforcing the screw thread so that forces applied to a graft bone block engaged with the screw thread will be buttressed by the aforesaid buttress construction forming a part of the screw thread construction.
It is a further object of the invention to provide both non-cannulated and cannulated versions of the inventive screws, as aforesaid.
It is a further object of the invention to provide an orthopedic interference screw, as aforesaid, which can be utilized in a medical procedure for endosteal fixation of a graft including the method step of selecting at least two different screws, one screw having buttressed threads oriented on an axially facing side facing toward the tip end of the screw and the other screw having buttress threads thereon which are each oriented on an axially facing side facing toward a head end of the screw.
It is a further object of the invention to provide a method of endosteal fixation, as aforesaid, wherein each of the screws is cannulated to facilitate installation of the respective screws utilizing a guide wire positioned through the osseous tunnel and each of the respective screws during the screw installation process.